This invention relates to an apparatus for modulating acceleration in the driving system of an automotive vehicle such as an automobile or a tractor provided with a hydraulic transmission.
Generally, a driving system for an automtive vehicle such as a tractor provided with a hydraulic transmission comprises an engine as a prime mover, a hydraulic pump driven by the engine to produce a hydraulic pressure, and a hydraulic motor connected through a hydraulic circuit to the pump so that the motor is driven by the output pressure of the pump to produce a motive force for driving the wheels of the vehicle. Either the pump or the motor or both are of a variable displacement type, so that the transmission ratio may be changed by changing the displacement of either or both of the pump and the motor.
In this system, the output of the engine is controlled by an accelerator provided with a pedal or the like in such a manner that the amount of operation applied to the accelerator pedal is transmitted through a displacement transmitting element such as a wire to the throttle valve of a carburetor for the engine.
Normally, the system of the above type is used in the range in which the output pressure of the hydraulic pump remains lower than the relief pressure of the hydraulic circuit including the pump and the motor. Under the normal condition, the absorption torque is the product of the output pressure of the pump and the displacement thereof.
In a system in which the outupt of the engine can be freely controlled by stepping on the accelerator pedal, it often happens that the output of the engine is increased to such an unnecessarily high level that the pressure in the hydraulic circuit reaches the relief pressure, whereupon the excess hydraulic operating fluid is discharged out of the circuit through a relief valve, with resulting waste of energy and abnormal rise of the temperature of the hydraulic operating fluid. This is a great disadvantage.
The object of the invention is to provide an apparatus for modulating acceleration in the driving system of an automotive vehicle, which completely eliminates the above-mentioned and other disadvantages of the conventional systems.
The invention will be described with reference to the accompanying drawings .